The use of late transition metal complexes as catalysts for olefin polymerization has recently been reviewed by Ittel et al. (Chem. Rev. 2000, 100, 1169). Notwithstanding the many advances described therein, there remains a need for new late transition metal catalysts with improved productivities under commercial reactor operating conditions, and for new methods of microstructure control. Late transition metal catalysts and processes that combine (i) high productivities at elevated temperatures and pressures in the presence of hydrogen as a molecular weight control agent, and (ii) high levels of branching, are especially sought. New catalysts and processes for these purposes are described herein.
The distribution of branch lengths obtained using late transition metal catalysts is also important. Previously reported catalysts have tended to give ethylene homopolymers with too few longer branches, relative to methyl branches, to give LLDPE's with adequate film toughness. With the objective of addressing this problem, we have developed catalysts and processes which give ethylene homopolymers with substantially higher ratios of C5 and longer branches to methyl branches. These new catalysts, processes and ethylene homopolymer compositions are also described herein.